Optical fibre communication systems often have to operate in harsh conditions and environments. The cables and the connectors that join the cable lengths together need to be of a rugged construction. It is seen as an advantage if the connectors are hermaphroditic, so that all plug and bulkhead connectors can mate together without the need for adapters. This advantage is not limited to optical systems as it will be appreciated that hermaphroditic connectors have applications in many systems including electrical and/or hybrid electrical and optical systems.
Harsh environment optical connectors have been used for about twenty years, principally for military applications. A typical commercial connector is hermaphroditic, with each half connector comprising two protruding lugs that mate with each other. The lugs are substantially diametrically opposed to one another with each lug having a screw thread on the outside. During the mating process the lugs on each half connector combine to form a cylindrical inner sleeve which may be brought into axial alignment by the securing in position of the lugs using a tube on the outside of each connector half. The engagement of the tube on the outside with the threads on the opposite half connector draws the optical components into alignment as the outer tubes are drawn into the locked position.
The provision of two diametrically opposed lugs on each connector half results in the possibility of the connector halves being connected in one of two possible positions, each position approximately 180° opposed to the other position. Manufacturers typically obviate this possibility by producing the lugs of non-equivalent dimensions such that the inner cylindrical sleeve is only achieved when the lugs are presented in a single position. Although this ensures that the connector halves can only achieve mating in one position, it does introduce difficulties in “blind mating” situations.
A further problem with the known connectors is that the locking mechanism is achieved by independent rotation and threading of a locking sleeve with the threads on the lugs or the opposing half connector. This requires a double action locking mechanism; the securing of a first connector outer sleeve to the inner lugs of the second connector, followed by the securing of the second connector outer sleeve to the inner lugs of the first connector.
Yet a fiber problem with known connectors is the fact that the locking of the sleeve about the lug is not part of the mating procedure, i.e. the opposing lugs are mated and it is the subsequent rotation and screwing of the sleeve onto the lug that achieves the locking. There is, therefore, no specific relationship between the axial alignment and the locking of the opposing half connectors, which may result in the user achieving incomplete locking, although axial alignment of the inner lugs is achieved, or complete locking and inadequate axial alignment.
Examples of such known connectors include those described in EP-A-0 114 230 and EP-A-0 166 636, EP-A-0 114 230 discloses an arrangement wherein initial location is provided by means of a pin in a socket, with locking of the two connectors being achieved by rotation of grip rings. FP-A-0 166 636 describes an arrangement which effects location of two opposing connectors using tapered lugs, and once located the rotation of grip rings serves to tighten the tapers against one another.
Heretofore have been described known external connectors and the problems associated therewith. Although there are problems in connector systems with providing a rugged connection suitable for harsh conditions that can be closed or opened easily when required, additional problems arise when aligning the components within the connectors so as to achieve optimum alignment/interengagement between related components when the two connector half portions are connected so as to form a sealed connector. Typically, the components are housed within an insert member, opposing insert members coming into interengagement once the connector half portions are connected so as to form the sealed connector. In known systems this alignment of the opposing members is achieved using a pin and socket arrangement, wherein one of the insert members comprises a pin which is adapted to be received within a socket of the opposing insert member.
This known pin and socket arrangement serves to align, within optical systems, the optical channels both axially and angularly. The insert member is machined to extremely fine tolerance and it achieves the required level of perpendicularity between the front mating surface and the channel bores because it is machined in one single operation. In order to protect the optical elements from contamination each channel typically has a coated glass window in a screw housing. The pin and socket are not easy to keep clean, and the pin is also prone to damage and as a result tends to seize up in its socket, which prevents the connector from de-mating.
The above pin and socket arrangement is typically used within optical applications for expanded beam connectors. In such expanded beam connectors or lens connectors a polished optical fibre end is supported in a ferrule and is aligned axially with a lens to produce an expanded beam that passes between the two halves of the connector and is focused down through another lens onto the receiving fibre end surface. An alternative method of transmitting light between two connector half portions is to use a butt joint connection. Butt joint connections comprise two opposing optical fibres each being supported in a ferrule, and when the fibre emerges from the ferrule end it is polished to provide a surface which is suitable to transfer light onto the opposing equivalent fibre end in the other half portion. In use, the two ferrules are axially aligned and positioned such that the two fibre ends are in contact. When aligning opposing insert members which house the ferrules supporting the fibres, known methods typically employ a sleeve to align the two mating ferrules. This results in very low loss coupling, provided that there is no contamination. However, it is difficult to clean inside an alignment sleeve, which is why this type of connection has normally only been used in clean environments.
The expanded beam method traditionally has been used in harsh environment applications since the expanded beam gives a better chance of transmitting light in the presence of contamination, whereas in alternative butt joint connections even small particles of dust may reduce the transferred optical power to unacceptably low levels. Problems with expanded beam include the fact that, as they are extremely sensitive to angular misalignment, excess loss is often caused by an accumulation of axial errors among the optical elements involved, which leads to angular misalignment.
There is therefore a requirement to provide an improved alignment means for aligning two opposing insert members when connecting them together into a sealed connector.